A public inquiry into plans for a bypass between Caernarfon and Bontnewydd in Gwynedd is expected to start in June.
Work on the new six mile (10km) road could start in the autumn once the inquiry has been completed.
The Welsh Government published draft orders last year, allowing people to submit objections to the route.
The cabinet secretary for economy and infrastructure has now agreed to hold the public inquiry.
A Welsh Government spokesman said: "It is anticipated the pre-inquiry meeting will take place on the week commencing 24 April and the Public Local Inquiry on the week commencing 12 June."
Arfon AM Sian Gwenllian welcomed the announcement and said: "The uncertainty has been very stressful for those who live along the route who are directly affected by the scheme and the uncertainty has meant delays in setting the building work in motion."